Formation of N-heterocyclic complexes of rhodium and palladium from a pincer silver(I) carbene complex

The pincer ligands 2,6-bis(n-butylimidazoliummethyl)pyridine dihalide (halide = Cl (3a), Br (3b) are easily obtained by the reaction of n-butylimidazole with 2,6-bis(chloromethyl)pyridine and 2,6-bis(bromomethyl)pyridine in a 2:1 molar ratio, respectively. Ligand 3a readily reacts with Ag2O in CH2Cl2 to yield the bis(Silver carbene) complex [2,6-bis(n-butylcarbenemethyl)pyridine][AgCl](2) (4) in 70% yield. The reaction of 4 with (PhCn)(2)PDCl2 in CH2Cl2 yields the palladium carbene complex Pd[2,6-bis(N-n-butylcarbenemethyl)pyridine]Cl-2 (5). The reaction of equimolar amounts of 4 and [Rh(COD)Cl](2) (COD = cyclooctadiene) in CH2Cl2 gave the dirhodium(I) complex [2,6-bis(N-n-butylcarbenemethyl)pyridine][Rh(COD)Cl](2) (6). All compounds were characterized by H-1 and C-13 NMR spectroscopy. The solid-state structures of 4 and 6 were determined by X-ray crystallography.